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How to keep a pool from getting algae. Solutions for a green pool. Keeping algae out of my pool

Updated on June 23, 2013

Why am I getting algae in my pool?

If you are experiencing algae problems on a regular basis, chances are your water is not balanced correctly. You've shocked it, added algaecide, keep chlorine tablets in it yet you are still having problems with algae. It is a chemistry issue. You should be able to keep algae out of a pool with only a 1.0 - 2.0ppm (parts per million) chlorine reading. There are a number of things I will cover here on water chemistry. You should know that chlorine and pH will be talked about very little in this section, as your algae problems most likely have very little to do with either. (unless you haven't added chlorine at all, that would certainly be a problem)

You can also get more information on algae problems with spas by clicking here

What is algae?

I will cover only two of the three common types of algae for now. Green algae and yellow (mustard) algae. These can be caused by a number of things, the first being low chlorine or sanitizer.

Green algae is a free floating algae. While it may hover slightly around the sides of a pool or the steps, it is not actually attached to anything. Green algae is most common because it is very opportunistic, meaning any faltering in your pool's chemistry or care will usually spark green algae's presence.

Yellow or mustard algae is similar to green algae but lacks chlorophyll, the chemical that produces the green pigment in plants. This algae is less common because it takes a longer time to develop. However, once mustard algae takes a hold, it can be difficult to treat, sometimes requiring multiple treatments to fully eliminate.

I will cover black algae in another hub.

pool with algae
pool with algae

How to prevent algae

Once you have cleaned and treated your pool (see link below "how to turn your swimming pool from green to clean" if you haven't done this yet) Have the water tested. Most pool stores will do this for you at no charge. What are your chemical readings? Chlorine should be between 2.0 and 5.0ppm(parts per million) If you've just treated your pool or turned over a green pool it may be higher than this. It will come down on it's own. pH should be between 7.4 - 7.6 ideally. If it is too high or low, based on the gallon size of your pool they will be able to tell you how much of what product to add, (i.e. muriatic acid to lower or sodium bicarbonate to raise depending on your alkalinity reading) Alkalinity should be between 80 - 120ppm.

Those are the three major chemical components you will test for on a regular basis. For recurring algae problems make sure to have your water tested for the following:

- Phosphates

-Cyanauric acid

I've had the water tested, now what?

Once your Chlorine, pH and Alkalinity are within recommended range, there are two things here that could potentially cause you some problems.

Phosphates: Phosphorus commonly enters the pool through wind drift (Do you have a lawn company that sprays near the pool? Phosphates can drift into the water which algae feeds on) If the phosphate level is high you will need a bottle of phosphate remover such as "PhosFree" which can be purchased through ad links on this sight.

Cyanuaric Acid: This is one of the most common problems I run into. If your pool uses Chlorine tablets, you will eventually have this problem. If you have a salt generator it won't be an issue. Cyanauric acid, or "stabilizer" are in Chlorine tablets. The water is being fed a continuous amount of stabilizer. It's very common to over stabilize the water. This doesn't happen overnight, it can be a year before the over-stabilization takes place. This means that even though you are getting a high chlorine reading, the chlorine molecules have been locked by the stabilizer and is now no longer effective as a sanitizer causing algae to feed. In order to correct this problem, the water will need to be diluted. There is no chemical on the market that reduces stabilizer. It can be added, but not removed except by diluting the water. (this is done by draining a few feet of water from pool and adding fresh. High calcium and high stabilizer are pretty much the two things that can't be fixed by adding a different chemical.


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  • robhampton profile image

    Rob Hampton 3 years ago from Tampa Bay, Florida

    Hey Chad, thanks for the comment. You will raise the alkalinity using sodium bicarbonate (baking soda) don't confuse this with soda ash which is used for pH. If your alkalinity is very low, you can use quite a bit of bicarbonate. It's not a harsh chemical and takes quite a bit to raise alkalinity. Start by diluting 2 pounds in a bucket of water and throwing it in the pool. Let circulate for a few hours then retest. Add as needed. Muriatic acid will lower alkalinity, but is a double edged sword as it will also drop the pH. High alkalinity will usually come down on its own if the pH is balanced.

  • profile image

    Chad 3 years ago

    How would one go about raising or lowering alkalinity? I see the test for it but no cure.


  • profile image

    Premier Robotic 4 years ago

    Invest in a good robotic pool cleaner! This will not only prevent an algae attack from coming on, but also if you have a really GOOD cleaner, it can help treat an attack already underway.

    Personally, I use the Dolphin Premier by the folks at Maytronics. It has tons of features I haven't seen on others (smart nav technology, a 360 degree cable swivel, multimedia options and much more...) and it actually does a good job on the waterline and algae-- something I haven't seen in many others out there.

    So if you're interested, check them out at!

    Thanks for the post.